Principal elements of English law
England's most authoritative law is statutory legislation, which comprises Acts of Parliament, regulations and by-laws. In the absence of any statutory law, the common law with its principle of stare decisis forms the residual source of law, based on judicial decisions, custom, and usage.
Common law is made by sitting judges who apply both statutory law and established principles which are derived from the reasoning from earlier decisions. Equity is the other historic source of judge-made law. Common law can be amended or repealed by Parliament.
Not being a civil law system, English law has no comprehensive codification. However, most of its criminal law has been codified from its common law origins, in the interests both of certainty and of ease of prosecution. For the time being, murder remains a common law crime rather than a statutory offence. 
Although Scotland and Northern Ireland form part of the United Kingdom and share Westminster as a primary legislature, they have separate legal systems outside of English Law.
International treaties such as the European Union's Treaty of Rome or the Hague-Visby Rules have effect in English law only when adopted and ratified by Act of Parliament. Adopted treaties may be subsequently denounced by executive action.